Attachable Matter Detection Apparatus

1. An attachable matter detection apparatus comprising a controller configured to function as: a decision part that decides a representative edge direction using a predetermined angle range as a unit for each pixel area of a plurality of pixel areas of a photographic image photographed by a camera, the representative edge direction being determined for each of the pixel areas based on an edge angle of each pixel contained in the pixel area; an extractor that extracts two of the pixel areas that are adjacent to each other as a pair area among the pixel areas of the photographic image, when the two pixel areas that are adjacent to each other have opposite representative edge directions; and a determination part that determines whether or not there is an attachable matter on a lens of the camera based on at least one of (1) a number of the pair areas extracted by the extractor and (2) a total sum of edge intensities of the pixel areas contained in the pair areas.

2. The attachable matter detection apparatus according to claim 1 , wherein the determination part determines that a non-attached state exists in which there is no attachable matter on the lens when at least one of the number of the pair areas and the total sum of the edge intensities of the pixel areas contained in the pair areas is equal to or more than a first predetermined threshold value.

3. The attachable matter detection apparatus according to claim 2 , wherein the determination part determines that a partially attached state exists in which the attachable matter is attached partially on the lens when at least one of the number of the pair areas and the total sum of the edge intensities of the pixel areas contained in the pair areas is less than the first predetermined threshold value and equal to or more than a second predetermined threshold value.

4. The attachable matter detection apparatus according to claim 3 , wherein the determination part determines that an entirely attached state exists in which the attachable matter is attached on an entirety of the lens when at least one of the number of the pair areas and the total sum of the edge intensities of the pixel areas contained in the pair areas is less than the second predetermined threshold value and equal to or more than a third predetermined threshold value.

5. The attachable matter detection apparatus according to claim 1 , wherein the decision part decides (A) a first representative edge direction using a first angle range as a unit for each of the pixel areas and (B) a second representative edge direction using a second angle range different from the first angle range as a unit for each of the pixel areas, and the extractor extracts the two pixel areas that are adjacent to each other as the pair area when at least one of the following conditions is met: (i) the respective first representative edge directions of the two pixel areas are opposite to each other; and (ii) the respective second representative edge directions of the two pixel areas are opposite to each other.

6. An attachable matter detection method comprising the steps of: (a) deciding, by a controller, a representative edge direction using a predetermined angle range as a unit for each pixel area of a plurality of pixel areas of a photographic image photographed by a camera, the representative edge direction being determined for each of the pixel areas based on an edge angle of each pixel contained in the pixel area; (b) extracting, by the controller, two of the pixel areas that are adjacent to each other as a pair area among the pixel areas of the photographic image, when the two pixel areas that are adjacent to each other have opposite representative edge directions; and (c) determining, by the controller, whether or not there is an attachable matter on a lens of the camera based on at least one of (1) a number of the pair areas extracted by the step (b) and (2) a total sum of edge intensities of the pixel areas contained in the pair areas.